The role of cell surface components in the initial recognition and interaction of nerve and muscle cells will be tested in cell culture. Two approaches will be used to identify components which may mediate recognition. In the first approach, labelled protein preparations from neuronal cells will be incubated with monolayers of cultured muscle and control cells. After washing the monolayer will be solubilized and the neuronal proteins which bind analyzed by SDS polyacrylamide gels. Proteins which appear to bind specifically to muscle will be purified, characterized, and used to produce monoclonal antibodies. In the second approach, monoclonal antibodies will be produced to neuronal cells capable of neuromuscular synapse formation. These will be used to detect surface components unique to these cells. This approach has previously been used to define 2 nervous system specific cell surface antigens, Band 1 and the G5 antigen. Band 1 will be purified to homogeneity from mouse brain and characterized in detail by biochemical and immunologic methods. Its distribution among neuronal cells and at CNS and neuromuscular synapses will be determined. Analogous studies will be performed on the G5 antigen. Monoclonal antibodies to Band 1, G5 and all other components of interest detected by the two approaches will be used to "block" nerve-muscle recognition in vitro. The primary assay will be analysis of the restriction of acetylcholine receptor to the point of nerve-muscle contact in the presence of Fab fragments from experimental and control antibodies. This combined analysis of apparent binding affinity, cellular distribution and presence at junctions and also antibody "block" experiments should establish the role of individual neuronal surface components in nerve-muscle recognition.